Photoinitiator, novel compound, and photocurable composition

ABSTRACT

A photoinitiator is provided which exhibits excellent photosensitivity, yields colorless products, and is usable in thick layer UV curable coating. A novel chemical compound is also provided which is usable for the photoinitator. Photocurable composition is also provided which has these properties. The photoinitiator consists essentially of a compound having a molecular weight of 1000 or less, and having a chemical structure represented by the following formula (1),  
                 
 
wherein R 3  and R 4  independently denote a specific alkyl group, and R 1  and R 2  independently denote an electron attracting group or a specific alkyl group, and weight percentage of a chemical structure element represented by the following formula (2),  
                 
which is expressed in formula (1) based on the total molecular weight of the compound, is 17% to 54% by mass.

TECHNICAL FIELD

The present invention relates to photoinitiators, a novel compound, andphotocurable compositions including a photoinitiator. More specifically,the present invention relates to photoinitiators which are usable inthick-layer UV curable coatings.

BACKGROUND ART

In recent years, photoinitiators are gaining in importance in the fieldof UV-light and daylight curable resin compositions, such asphotocurable coatings or photocurable printing inks, which may beapplicable to a wide range of substrates including metal, paper,plastics and wood, since the photoinitiators can drastically increasecuring rate.

In this field, highly sensitive photoinitiators are desired, which arecapable of absorbing enough UV or daylight, and producing radicals thatstart polymerization or transferring the absorbed energy topolymerizable substances for formation of radicals.

Conventionally, photoinitiators have been repeatedly studied so far withthe aim of enhancing sensitivity, and improving inherent technicalproblems such as yellowing. In order to overcome these general problems,for example, alkylphenylbisacrylphosphine oxides, and photoinitiatormixtures of an alkylphenylbisacrylphosphine oxide with benzophenone aredisclosed in U.S. Pat. No. 6,020,528.

The conventional photoinitiators, such as alkylphenylbisacylphosphineoxides exhibit a good curability, particularly when used in thin layerphotocurable coatings. However, the photoinitiators are difficult to usefor UV curing of coatings having a greater layer thickness. This isbecause the self-absorption of the photoinitiator molecule containingaromatic structure elements is large.

Furthermore, the photoinitiators of the alkylphenylbisacylphosphineoxide type exhibit an improved yellowing behavior in comparison withother conventional photoinitiators (e.g., benzophenone). However, theproblem of yellowing has not been completely solved thus far. Therefore,there is a strong need for a photoinitiator showing significantimprovement regarding yellowing.

DISCLOSURE OF INVENTION

It is therefore an object of the invention to provide a photoinitiatorwhich exhibits excellent photosensitivity, yields colorless products,and is also usable in thick layer UV curable coatings.

Another object is to provide a novel chemical compound which is usablefor the photoinitator. Furthermore, another object is to provide aphotocurable composition having aforesaid properties.

Unexpectedly, the inventors have now found that a compound having achemical structure represented by the following formula (1) hasexcellent photoactivity with UV irradiation, and is well suited forphotopolymerization of radical curable ethylenic unsaturated compounds.

Accordingly, the present invention provides a photoinitiator consistingessentially of a compound having a molecular weight of 1000 or less, andhaving a chemical structure represented by the following formula (1),

-   -   wherein R₃ and R₄ independently denote an alkyl group having a        carbon number of 1 to 8, and    -   R₁ and R₂ independently denote    -   1) an electron attracting group,    -   2) an alkyl group having a carbon number of 1 to 8, or    -   3) an alkyl group having a carbon number of 1 to 8, which has an        electron attracting group at the β, γ, or δ position with        respect to both of the carbonyl groups, wherein the alkyl        group 2) is methyl or ethyl group when each of the two        substituents is the alkyl group 2), and    -   mass percentage of a chemical structure element represented by        the following formula (2),    -   which is expressed in formula (1), based on the total molecular        weight of the compound having the chemical structure represented        by formula (1), is within the range of 17% to 54%.

The present invention also provides a photoinitiator consistingessentially of a compound having a molecular weight of 1000 or less, andhaving a chemical structure represented by the following formula (3),

-   -   wherein R₃ denotes an alkyl group having a carbon number of 1 to        8, R₅ denotes a mono-, di-, tri-, tetra- or pentavalent        aliphatic hydrocarbon group or an alkyleneoxy group-substituted        aliphatic hydrocarbon group, n is a natural number of 1 to 5,        and    -   R₁ and R₂ independently denote    -   1) an electron attracting group,    -   2) an alkyl group having a carbon number of 1 to 8, or    -   3) an alkyl group having a carbon number of 1 to 8, which has an        electron attracting group at the β, γ, or δ position with        respect to both of the carbonyl groups, wherein the alkyl        group 2) is methyl or ethyl group when each of the two        substituents is the alkyl group 2), and    -   weight percentage of a chemical structure element represented by        the following formula (2),    -   which is expressed in formula (3), based on the total molecular        weight of the compound having the chemical structure represented        by formula (3), is within the range of 17% to 47%.

The present invention also provides a novel compound having a chemicalstructure represented by the following formula (7),

wherein

-   -   R₆ denotes an alkyl group having a carbon number of 1 to 8, a        C₁-₄ alkyl carbonyl group, a cyano group, a C₁₋₄ alkyl carbonyl        methyl group, a C₁-₄ alkyl carbonyl ethyl group, a C₁-₄ alkoxy        carbonyl methyl group, a C₁-₄ alkoxy carbonyl ethyl group, and        an alkyl group having a carbon number of 1 to 8 which is        substituted by carboxyl group or cyano group,    -   R₇, R₈, R₉, and R₁₀ independently denote a hydrogen atom, or a        methyl group, and at least one of R₉ and R₁₀ is a hydrogenatom,    -   R₁₁ denotes a di-, tri- or tetra-valent aliphatic hydrocarbon        group having a carbon number of 2 to 12,    -   R₁₂ denotes a methyl group, or an alkoxy group having a carbon        number of 1 to 18,    -   n is a natural number of 2 to 4, and    -   m is an integer of 0 to 15.

The present invention also provides a photocurable compositioncomprising,

-   -   an above-mentioned photoinitiator, and    -   a radical curable ethylenic unsaturated compound.

BEST MODE FOR CARRYING OUT THE INVENTION

R₃ and R₄, defined as an alkyl group having a carbon number of 1 to 8 inthe aforementioned chemical structure represented by formula (1) or theaforementioned chemical structure represented by formula (3), may be alinear or branched alkyl group, which include methyl, ethyl, propyl,isopropyl, n-butyl, t-butyl, pentyl, hexyl, cyclohexyl, n-heptyl, andn-octyl groups. Among these structures, in particular, a methyl group ispreferable from the veiwpoints of photosensitivity.

R₅, defined as an aliphatic hydrocarbon, includes a linear or branchedalkyl group such as methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl,pentyl, hexyl, cycro-hexyl, n-heptyl, n-octyl, and a multi-functionalaliphatic hydrocarbon group such as ethylene, propylene, trimethylolpropane residual group, or pentaerythritol residual group.

R₅, defined as an alkyleneoxy group-substituted aliphatic hydrocarbongroup, includes an alkyl group obtained by a reaction of methanol,ethanol, propanol, isopropanol, n-butanol, t-butanol, pentanol, hexanol,cyclohexanol, n-heptanol, n-octanol, ethylene glycol, propylene glycol,neopentyl glycol, trimethylol propane, or pentaerythritol and ethyleneoxide or propylene oxide.

R₁ and R₂ in the aforementioned chemical structure represented byformula (1) or the aforementioned chemical structure represented byformula (3) is selected from the group consisting of

-   -   1) an electron attracting group,    -   2) an alkyl group having a carbon number of 1 to 8, and    -   3) an alkyl group having a carbon number of 1 to 8, which has an        electron attracting group at the β, γ, or δ position with        respect to both of the carbonyl groups.

Examples of the electron attracting groups 1) include a ketone groupsuch as acetyl group, an ester group, an ether group, a carboxyl group,a cyano group, a sulfonic acid group, a sulfonyl group, or a phosphategroup.

The definition of alkyl group 2), having a carbon number of 1 to 8, isthe same as the definition of the above-mentioned R₃ or R₄.

The alkyl group having a carbon number of 1 to 8, which has an electronattracting group at the β, γ, or δ position with respect to both of thecarbonyl groups 3) include the following structures.[β position substituted groups]

[γ position substituted groups]

[β position and γ position substituted group]

[δ position substituted groups]

Here, the γ position substituted group No. 12 may be connected withanother β-dicarbonyl units via an alkylene group, a poly(alkyleneoxy)alkylene group, or a residual structure of poly-functional archol.

In this invention, these groups may be selected randomly as R₁ or R₂;however, when each of the two substituents is the alkyl group 2), methylor ethyl group must be selected as the alkyl group 2) in order toproduce at least one radical by photoirradiation.

Among these above-mentioned groups, particularly preferred groups areNos. 4, 5 and 12, from the viewpoint of photosensitivity as well astheir ease of production.

In this invention, the compound having the chemical structurerepresented by formula (1) or the aforementioned chemical structurerepresented by formula (3), is characterized in having a molecularweight of 1000 or less, that is, a compound having the molecular weightrange is usable as an additive type photoinitiator, and furthermore,exhibits good compatibility with radical curable monomers, oligomers, orpolymers. Furthermore, a compound having a molecular weight in the aboverange can give its cured products hardness and solvent resistance.

The preferable range of the molecular weight is 700 or less, from theviewpoint of the compatibility, and also from the viewpoint of hardnessand solvent resistance of a cured composition which contains thecompound.

Furthermore, the compound having the chemical structure represented byformula (1) or the chemical structure represented by formula (3), ischaracterized in that the mass percentage of a chemical structureelement represented by the following formula (2),

which is expressed in formula (1) or formula (3), based on the totalmolecular weight of the compound, is within the range of 17% to 54% bymass. The excellent photosensitivity of the present invention resultsfrom the above range of the mass percentage of the chemical structureelement represented by formula (2).

Examples of the compound having the chemical structure represented byformula (1) are

-   -   3,3-Dimethyl-2,4-pentandione,    -   3,3-Diethyl-2,4-pentandione,    -   3-Acetyl-3-methyl-4-oxo-pentanoic acid ethyl ester,    -   4-Acetyl-4-methyl-5-oxo-hexanoic acid ethyl ester,    -   4-Acetyl-4-methyl-5-oxo-hexanoic acid butyl ester,    -   4-Acetyl-4-methyl-5-oxo-hexanoic acid hexyl ester,    -   4-Acetyl-4-methyl-5-oxo-hexanoic acid octyl ester,    -   4-Acetyl-4-methyl-5-oxo-hexanoic acid cyclopentadienyl ester,    -   4-Acetyl-4-methyl-5-oxo-hexanoic acid (2-hydroxyethyl) ester,    -   4-Acetyl-4-methyl-5-oxo-hexanoic acid cyclopentadienyl ester,    -   4-Acetyl-4-methyl-5-oxo-hexanoic acid isobornyl ester,    -   5-Acetyl-5-methyl-6-oxo-heptanoic acid ethyl ester,    -   Diethyl 2,2-diacetyl-1,5-pentanedioate represented by the        following formula,    -   3,3-Diacetyl-hexanedioic acid diethyl ester represented by the        following formula,    -   4,4-Diacetyl heptanedioic acid 1,7-diethyl ester    -   4,4-Di-(1-oxopropyl)-heptanedioic acid 1,7-dimethyl ester    -   3,3-Diacetyl-1,5-dicyanopentane,    -   5,5-Diacetyl nonane-2,8-dione,    -   4,4-Diacetyl-heptanedioic acid 1,7-di-tert-butyl ester    -   4,4-Diacetyl-1,7-heptanedioic acid    -   3,3-Diacetyl-1,5-bis(methylsulfonyl)-pentane    -   4,4-Diacetyl-7-oxo-octanoic-ethyl ester    -   4,4-Diacetyl-5-(ethoxycarbonyl)-heptanedioic acid diethyl ester        represented by the following formula,    -   a compound having two β-dicarbonyl groups such as        3-{4-Acetyl-4-[2-(ethoxycarbonyl)ethyl]-5-oxohexanoyloxy}-2,2-dimethylpropyl        ethyl 4,4-diacetylheptane-1,7-dioate represented by the        following formula,    -   a compound having three β-dicarbonyl groups such as        2,2-Bis({4-acetyl-4-[2-(ethoxycarbonyl)ethyl]-5-oxohexanoyloxy}methyl)butyl        ethyl 4,4-diacetylheptane-1,7-dioate represented by the        following formula,

Examples of the compound having the chemical structure represented byformula (3) are

-   -   2-Acetyl-2-ethyl-pentanedioic acid 1,5-diethyl ester,    -   Diethyl 2-acetyl-2-(ethoxycarbonyl)-1,5-pentanedioate        3-Acetyl-3-(ethoxycarbonyl)-pentanedioic acid 1,5-dimethyl ester    -   2-Acetyl-2-(ethoxycarbonyl)-hexanedioic acid 1,6-dimethyl ester    -   4-Acetyl-4-(methoxycarbonyl)-heptanedioic acid 1,7-dimethyl        ester,    -   4-(Methoxycarbonyl)-4-(1-oxopropyl)-heptanedioic acid        1,7-dimethyl ester,    -   4-(Ethoxycarbonyl)-4-(2-methyl-1-oxopropyl)-heptanedioic        acid-1,7-dimethyl ester    -   4-(Ethoxycarbonyl)-4-(1-oxobutyl)-heptanedioic acid 1,7-dimethyl        ester    -   4-Acetyl-4-(methoxycarbonyl)-octanedioic acid 1,8-dimethyl ester    -   4-Acetyl-4-(tert-butoxycarbonyl)-heptanedioic acid 1,7-dimethyl        ester    -   a compound having two β-dicarbonyl groups such as Dimethyl        4-acetyl-4-[(3-{2,2-bis[2-(methoxycarbonyl)ethyl]-3-oxobutanoyloxy}-2,2-dimethylpropyl)oxycarbonyl]heptane-1,7-dioate        represented by the following formula,

Among these examples, the compounds having the chemical structurerepresented by formula (1) are preferred due to their excellentphotosensitivity. Furthermore, the compounds having identicalsubstituents at α-position of β-dicarbonyl structure are particularlypreferred as well. From the viewpoint of ease of production, thecompounds only having the above-mentioned γ position substituted groupNos. 4, 5, 12 are particularly preferred.

The novel compound of the present invention has the chemical structurerepresented by the following formula (7).

In these formulas, R₆ is selected from the group consisting of

-   -   an alkyl group having a carbon number of 1 to 8, a C1-4 alkyl        carbonyl group, a cyano group, a C1-4 alkyl carbonyl methyl        group, a C1-4 alkyl carbonyl ethyl group, a C1-4 alkoxy carbonyl        methyl group, a C1-4 alkoxy carbonyl ethyl group, and a alkyl        group having a carbon number of 1 to 8 which is substituted by        carboxyl group or cyano group.

The definition of the alkyl group having a carbon number of 1 to 8 isthe same as the definition of the above-mentioned R₃ or R₄.

The C1-4 alkyl carbonyl group includes acetyl group, ethyl carbonylgroup, propyl carbonyl group, or butyl carbonyl group.

The C1-4 alkyl carbonyl methyl group includes 2-oxopropyl group,2-oxobutyl group, 2-oxopentyl group, and 2-oxohexyl group.

The C1-4 alkyl carbonyl ethyl group includes 3-oxobutyl group,3-oxopentyl group, 3-oxohexyl group, and 3-oxoheptyl group. The C1-4alkoxy carbonyl methyl group includes methoxy carbonyl methyl group,ethoxy carbonyl methyl group, propoxy carbbnyl methyl group, butoxycarbonyl methyl group.

The C1-4 alkoxy carbonyl ethyl group includes methoxy carbonyl ethylgroup, ethoxy carbonyl ethyl group, propoxy carbonyl ethyl group, butoxycarbonyl ethyl group.

The alkyl group having a carbon number of 1 to 8 which is substituted bycarboxyl group or cyano group includes carboxyl group- or cyanogroup-substituted methyl groups, ethyl groups, propyl groups, isopropylgroups, n-butyl groups, t-butyl groups, pentyl groups, hexyl groups,cyclohexyl groups, n-heptyl groups, n-octyl groups.

R₇, R₈, R₉, and R₁₀ independently denote hydrogen atom, or a methylgroup. Here, at least one of R₉ or R₁₀ is a halogen atom.

R₁₁ denotes a di-, tri-, tetra-valent aliphatic hydrocarbon group havinga carbon number of 2 to 12. Examples of the R₁₁ are ethylene, propylene,trimethylol propane residual group, and pentaerythritol residual group.Here, n is an integer of 2 to 4, and m is an integer of 0 to 15.

Furthermore, R₁₂ denotes a methyl group, or an alkoxy group having acarbon number of 1 to 18.

Examples of the alkyoxy group include a linear or branched alkoxy groupsuch as methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, t-butoxy,pentyl-oxy, hexyl-oxy, cycrohexyl-oxy, n-heptyl-oxy, n-octyl-oxy,decyl-oxy, undecyl-oxy, lauryl-oxy, tridecyl-oxy, myristyl-oxy,pentadecyl-oxy, cetyl-oxy, heptadecyl-oxy, and stearyl-oxy.

Among these novel compounds, the compounds having a molecular weight of1000 or less are preferable as well as the above-mentionedphotoinitiators from the viewpoints of compatibility and the curedproduct properties. Furthermore, it is particularly preferred that thenovel compounds have the chemical structure element represented byformula (2) at the rate of 17% to 54% by mass from the viewpoint of itsphotosensitivity if R₁₂ is a methyl group. On the other hand, if R₁₂ isan alkoxy group having a carbon number of 1 to 18, the range of 17% to47% by mass of the content of the chemical structure element representedby formula (2) is preferable.

Moreover, in the chemical structure represented by formula (7) or (8),formulas of m=0 are preferable from the viewpoints of balance of theirmolecular weight and the content of the chemical structure elementrepresented by formula (2).

Some of the above-mentioned examples belong to the preferable novelcompounds of the present invention such as3-{4-Acetyl-4-[2-(ethoxycarbonyl)ethyl]-5-oxohexanoyloxy}-2,2-dimethylpropylethyl 4,4-diacetylheptane-1,7-dioate represented by the followingformula,

a compound having three β-dicarbonyl groups such as2,2-Bis({4-acetyl-4-[2-(ethoxycarbonyl)ethyl]-5-oxohexanoyloxy}methyl)butylethyl 4,4-diacetylheptane-1,7-dioate represented by the followingformula,

These compounds can be prepared by standard well-known organicsyntheses, such as alkylation and Michael addition. The alkylation canbe carried out by the reaction of a β-diketone or a β-ketoester havingan acidic H atom with a halogenated alkane in the presence of a basecatalyst such as potassium carbonate. The Michael addition can becarried out by the reaction of a β-diketone or a β-ketoester having anacidic H atom with an ethylenic unsaturated compound having an electronattracting group in the presence of a base catalyst.

Among them, the Michael addition is particularly suitable for producingthe compounds of the present invention.

Examples of suitable ethylenic unsaturated compounds having an electronattracting group, hereinafter abbreviated to “activated vinyl compound”,as a starting material of the Michael addition are, for example, acrylicacid esters, methacrylic acid esters, acryl amide, N-vinyl pyrrolidoneor acrylonitirile.

Furthermore, specific examples thereof include, acrylic acid methylester, acrylic acid ethyl ester, acrylic acid butyl ester, acrylic acidhexyl ester, acrylic acid 2-ethyl hexyl ester, acrylic acid octyl ester,acrylic acid ethyl ester cyclopentadienyl ester, acrylic acid isobornylester, acrylic acid 2-hydroxyethyl ester, acrylic acid 2-hydroxypropylester, propylenglykol mono acrylic acid ester, acrylic acid2-carboxyethyl ester, acrylonitrile, vinyl methyl ketone and acrylamide.

Furthermore, in the case of producing a compound having at least twoβ-diketone units per molecule, preferable examples of activated vinylcompound include

-   -   1,2-ethanediol diacrylate, 1,2-propanediol diacrylate,        1,4-butanediol diacrylate, hexan-1,6-diol diacrylate,        dipropylene glycol diacrylate, neopentyl glycol diacrylate,        ethoxylated neopentyl glycol diacrylate, propoxylated neopentyl        glycol diacrylate, tripropylene glycol diacrylate, polyethylene        glycol diacrylate, trimethylolpropane triacrylate, ethoxylated        trimethylolpropane triacrylate, propoxylated trimethylolpropane        triacrylate, propoxylated glycerine triacrylate, tris        (2-acryloyloxy ethyl) isocyanurate, pentaerythritol triacrylate,        ethoxylated pentaerythritol triacrylate, pentaerythritol        tetraacrylate, ethoxylated pentaerythritol tetraacrylate, di        (trimethylolpropane) tetraacrylate, di (pentaerythritol)        pentaacrylate, di (pentaerythritol) hexaacrylate.

Examples of the β-diketone or β-ketoester having an acidic H atom,typically have two carbonyl groups at the 1,3-position and one orpreferably two acidic protons at the α position.

Examples of the compounds, which are suitable to synthesize thecompounds related to this invention, are pentane-2,4-dione,hexane-2,4-dione, heptane-2,4-dione, 1-methoxy-pentan-2,4-dion,propionyl acetic acid ethyl ester, propionyl. acetic acid butyl ester,butyryl acetic acid methyl ester, acetoacetic acid methyl ester,acetoacetic acid ethyl ester, acetoacetic acid isopropyl ester,acetoacetic acid butyl ester, acetoacetic acid tert-butylester,acetoacetic acid 2-methoxyethyl ester, acetoacetic acid 2-ethylhexylester, acetoacetic acid lauryl ester, 2-acetoacetoxyethyl acrylate,2-acetoacetoxyethyl methacrylate and acetoacetic acid benzyl ester.

Furthermore, in the case of producing a compound having at least twoβ-diketone units per molecule, preferable examples of activated vinylcompound include neopentyl glycol diacetoacetate,2-ethyl-2-butyl-1,3-propanediole diacetoacetate, cyclohexanedimethanolacetoacetate, trimethylolpropane triacetoacetate, glycerinetriacetoacetate, pentaerithritol triacetoacetate, pentaerithritoltetraacetoacetate, ditrimethylolpropane tetraacetoacetate, anddipentaerithritol hexaacetoacetate.

Furthermore, the β-ketoester includes a β-ketoester of an alkoxy alcholobtained by a reaction of methanol, ethanol, propanol, isopropanol,n-butanol, t-butanol, pentanol, hexanol, cyclohexanol, n-heptanol,n-octanol, ethlene glycol, propylene glycol, trimethylol propane, orpentaerythritol and ethylene oxide.

The Michael addition reaction of the activated vinyl compound with theβ-diketone or β-ketoester having an acidic H atom can be accelerated byspecial catalysts like strong bases and ammonium halides. The amount ofcatalyst used is within the range of 0.1 to.5.0 weight percent referredto the complete reaction mixture, preferably 0.4 to 2.0 weight percent.Reaction temperature is within the range of 25 to 150° C., preferably 50to 110° C. During the reaction of the activated vinyl compounds with theβ-diketone or β-ketoester having an acidic H atom, the reaction mixtureis sparged with air.

Additionally, a polymerization inhibitor can be used in order to avoidunwanted gelation caused by reactive vinyl compounds during synthesis.The amount is within the range of 0.01 to 0.5 weight percent. Suitablepolymerization inhibitors are, for example, 4-methoxy phenol,phenothiazin and hydrochinone. By the above described procedure,obtained products are either solid or liquid and can be purified byre-crystallization or distillation under reduced pressure.

The final product of the above-mentioned process is mainly obtained as acompound having a single, well-defined chemical structure. However, whenusing a poly-functional activated vinyl compound or a poly-functionalβ-diketone or β-ketoester mentioned above, the final product may beobtained as a mixture containing several structure compounds.

The photoinitiator according to this invention is usable for curing ofradical curable monomers, oligomers, or polymers.

That is, the photocurable composition according to the present inventioncomprises,

-   -   (i) an above-mentioned photoinitiator, and    -   (ii) a radical curable ethylenic unsaturated compound

An amount of the photoinitiator among the photocurable composition ispreferably within the range of 1 to 15 percent by weight. In particular,the amount is preferably within the range of 2 to 10 percent by weight.

Among the radical curable ethylenic unsaturated compounds, especiallythose which are activated by heteroatoms can be polymerized very well.Examples for this type of compounds are monomers such as acrylic acidesters, methacrylic acid esters, acrylonitrile, acryl amide, acrolein,vinyl acetate, vinyl propionate, N-vinyl pyrrolidone, N-vinyl carbazole,vinyl chloride and vinylidene chloride.

When using these monomers, the present composition can be obtained bydissolving the photoinitiator in the monomers. This is done by stirringor heating the mixture.

Furthermore, the radical curable ethylenic unsaturated compound alsoincludes a compound having two or more radical curable ethylenicunsaturated groups. Examples for these compounds are 1,2-ethanedioldiacrylate, 1,2-propanediol diacrylate, 1,4-butanediol diacrylate,hexan-1,6-diol diacrylate, dipropylene glycol diacrylate, neopentylglycol diacrylate, ethoxylated neopentyl glycol diacrylate, propoxylatedneopentyl glycol diacrylate, tripropylene glycol diacrylate, bisphenol Adiglycidylether diacrylate, ethoxylated bisphenol A diglycidyletherdiacrylate, polyethylene glycol diacrylate, trimethylolpropanetriacrylate, ethoxylated trimethylolpropane triacrylate, propoxylatedtrimethylolpropane triacrylate, propoxylated glycerine triacrylate,tris(2-acryloyloxy ethyl) isocyanurate, pentaerythritol triacrylate,ethoxylated pentaerythritol triacrylate, pentaerythritol tetraacrylate,ethoxylated pentaerythritol tetraacrylate, di(trimethylolpropane)tetraacrylate, di(pentaerythritol) pentaacrylate, di(pentaerythritol)hexaacrylate and oligomers and polymers containing acrylate groupsobtained by conversion of poly epoxides with acrylic acid (epoxyacrylate) or by conversion of polyester polyol with acrylic acid ormonomeric alkyl acrylates (polyester acrylates) or by conversion ofisocyanate prepolymers with 2-hydroxyethyl acrylate ((polyurea acrylate)and acrylated soy bean oil and acrylated silicone oil.

The composition of the present invention may contain anotherconventional photoinitiator as long as the effects of the presentinvention are not impaired.

The conventional photoinitiator includes benzophenone, Michler's ketone,dialkyl acetophenone, hydroxyalkyl acetophenone, aminoalkyl phenone,acylphosphine oxide and so called sensitizers such as isopropylthioxanthone and 3-keto cumarine.

Additionally the photocurable composition of the invention may containso called accelerators such as tributylamine, N-methyl diethanolamine,N-butyl diethanolamine, triethanolamine, piperidine, morpholine,piperazine, and acrylated amines, obtained from 1,6-hexanedioldiacrylate and ethanolamine.

In order to prevent inhibition of polymerization by oxygen, a waxycompound can be added in addition to the above components. Inconsequence of their appropriate solubility in the mixtures, they floaton top of the mixture at the start of polymerization and form a thinprotecting layer between atmospheric oxygen and the polymerizingmixture. Additionally, auto-oxidizing compounds like allyl ethers can beadded that prevent inhibition of polymerization by oxygen in some cases.

Furthermore, the photocurable composition may contain well knownadditives, for example, silica, cement, talcum, leveling agents, wettingagents like polyelectrolyte, degassers like poly siloxane copolymers,flow and fluxing agents, surfactants, delustering agents, andplasticizers such as a phthalate.

The photocurable composition according to this invention can be obtainedby mixing the foregoing respective components uniformly, and can becured by high-energy rays, preferably ultraviolet rays.

As radiation sources, sunlight or artificial irradiation generated bycommercial mercury high-, medium- or low-pressure lamps, or xenon orwolfram lamps, can be used. The wavelength of the applied irradiation iswithin a range of 200 to 500 nm, preferably 250 to 350 nm. Duration ofexposure depends on amount and type of the used photoinitiator and canbe selected from a fraction of a second to several minutes. In masspolymerization, exposure time can be within the range of hours as well.

EXAMPLES Example 1 3,3-Dimethyl-2,4-Pentandione

50 g of 2,4-pentandione, 178 g of iodo-methane, 120 g of potassiumcarbonate, and 340 ml of acetone were mixed and heated to reflux for 18hours. After cooling, 200 ml of petroleum ether was added, and the solidwas filtered off and washed with 300 ml of an one-to-one mixture ofpetroleum ether. Residual 3-methyl-2,4-pentandione was removed byreacting with ethyl acrylate. The raw product was distilled to yield 23g of 3,3-dimethyl-2,4-pentandione (boiling point: 63° C./20 mbar;purity: >99%; colorless).

Content of the active structural element C₃O₂: 54%.

Example 2 3,3-Diethyl-2,4-Pentandione

25 g of 2,4-pentandione, 98.3 g of-bromo-ethane, 80 g of potassiumcarbonate, and 175 ml of acetone were mixed and refluxed for 39.5 hours.The solid was filtered off and washed with petroleum ether and acetone.To the liquid layer, 2.0 g of 1,8-diazabicyclo-[5.4.0]-undec-7-ene wasadded and the mixture was refluxed for two days. After addition of anadditional 11.6 g of 1,8-diazabicyclo-[5.4.0]-undec-7-ene and refluxingfor seven hours, 25 g of ethyl acrylate was added and the mixture wasstirred at room temperature, and the solvent was distilled off and themixture was refluxed for 8 hours. The base was neutralized by addingacetic acid, washed with an aqueous potassium carbonate solution, andextracted with diethyl ether. The ether layer was dried and the productwas isolated by fractional distillation to yield 9 g of product (boilingpoint 190° C./1000 mbar; purity: 75%; colorless).

Content of the active structural element C₃O₂: 44%.

Example 3 3-Acetyl-3-Methyl-4-Oxo-Pentanoic Acid Ethyl Ester

28 g of potassium hydroxide dissolved in 28 ml of water was added to amixture of 50 g of 2,4-pentandione, and 100 ml and 115 ml of dioxane at0 to 10° C. After 20 minutes of stirring, 125 g of bromoacetic acidethyl ester was added dropwise and the mixture was stirred for 19 hours.The layers were separated and washed with water and diethyl ether. Theorganic layer was dried and 3-acetyl-4-oxo-pentanoic acid ethyl esterwas isolated by fractional distillation.

48.3 g of 3-acetyl-4-oxo-pentanoic acid ethyl ester, 41 g ofiodo-methane, 34 g of potassium carbonate, and 90 ml of acetone weremixed and refluxed for 9 hours. After cooling, 100 ml of petroleum etherwas added, and the solid was filtered off and washed with acetone andpetroleum ether. Fractional distillation yielded 33.4 g of3-acetyl-3-methyl-4-oxo-pentanoic acid ethyl ester (boiling point: 69°C./0.02 mbar; purity: 97%; colorless).

Content of the active structural element C₃O₂: 34%.

Example 4 4-Acetyl-4-Methyl-5-Oxo-Hexanoic Acid Ethyl Ester

51 g of 2,4-pentandione, 89 g of iodo-methane, 66 g of potassiumcarbonate, and 170 ml of acetone were refluxed for 7 hours, the mixturewas cooled, and 200 ml of petroleum ether was added. After filtration,the solid was washed with acetone and petroleum ether, and3-methyl-2,4-pentandione was isolated by fractional distillation.

30 g of 3-methyl-2,4-pentandione and 0.4 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene were mixed and 39.3 g of ethylacrylate was added dropwise with the temperature being controlled bycooling with ice. Stirring was continued for 16 hours, the base wasneutralized, 50 ml of diethyl ether was added, and the mixture wasextracted with an aqueous sodium carbonate solution and water.Fractional distillation of the organic layer yielded 33.4 g of4-acetyl-4-methyl-5-oxo-hexanoic acid ethyl ester (boiling point: 95°C./0.02 mbar; purity: 98%; colorless).

Content of the active structural element C₃O₂: 32%.

Example 5 5-Acetyl-5-Methyl-6-Oxo-Heptanoic Acid Ethyl Ester

10 g of sodium acetylacetonate and 20 g of potassium carbonate in 50 mlof acetone were heated to reflux and 15 g of bromoacetic acid ethylester was added dropwise over 15 minutes. After refluxing for severaldays, the solid was filtered off and washed with petroleum ether andacetone. Fractional distillation yielded 6.4 g of5-acetyl-6-oxo-heptanoic acid ethyl ester.

5.5 g of 5-acetyl-6-oxo-heptanoic acid ethyl ester, 5.7 g of potassiumcarbonate, 15 g of iodo-methane, and 15 ml of acetone were refluxed for18 hours. After cooling, petroleum ether was added, and the solid wasfiltered off and washed with acetone and petroleum ether. Fractionaldistillation and re-distillation yielded 5.11 g of5-acetyl-5-methyl-6-oxo-heptanoic acid ethyl ester (boiling point: 151°C./20 mbar; purity: 82%; colorless).

Content of the active structural element C₃O₂: 30%.

Example 6 2-Acetyl-2-Ethyl-Pentanedioic Acid 1,5-Diethyl Ester

10 g of 2-ethyl ethyl acetoacetate and 0.1 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene were mixed and 8 g of ethylacrylate was added at room temperature over 25 minutes. The mixture wasstirred for 23 hours, neutralized, poured into 20 ml of diethyl ether,and extracted with an aqueous potassium carbonate solution and water.Fractional distillation of the organic layer yielded 7.5 g of2-acetyl-2-ethyl-pentanedioic acid diethyl ester (boiling point: 145°C./20 mbar; purity: >99%; colorless).

Content of the active structural element C₃O₂: 27%.

Example 7 Diethyl 2,2-Diacetyl-1,5-Pentanedioate

5 g of sodium salt of ethyl acetoacetate was mixed with 30 ml oftoluene. Over 20 minutes, 5 g of acetic acid chloride was addeddropwise, and the mixture was stirred for one hour at room temperatureand at 85° C. for 3 hours. The solid was filtered off and washed withdiethyl ether. Fractional distillation of the liquid phase yielded ethyl2-acetyl-3-oxo-butyrate.

2.0 g of ethyl 2-acetyl-3-oxo-butyrate was mixed with 5 drops of1,8-diazabicyclo-[5.4.0]-undec-7-ene. Over 10 minutes, 2.7 g of ethylacrylate was added dropwise. The mixture was stirred for 30 hours atroom temperature, 2 ml of acetic acid was added to neutralize the base,and the mixture was extracted with an aqueous sodium carbonate solutionand water. Fractional distillation yields 1.5 g of2,2-diacetyl-1,5-pentanedioic acid diethyl ester (purity: 70%;colorless).

Content of the active structural element C₃O₂: 25%.

Example 8 Diethyl 2-Acetyl-2-(Ethoxycarbonyl)-1,5-Pentanedioate

60 g of diethyl 2-carboxyethyl-1,5-pentanoate was added drop by drop to10.44 g of sodium hydride covered by 100 ml of toluene. Whenheat-production ceased, 28 g of ethyl chloroformate was added dropwise.When maximum conversion was reached, the pH value was adjusted to 7 byadding hydrochloric acid, the salt was filtered off and the residualliquid fractionated under reduced pressure to yield diethyl2-acetyl-2-(ethoxycarbonyl)-1,5-pentanedioate (purity: 85%; colorless).

Content of the active structural element C₃O₂: 23%.

Example 9 3,3-Diacetyl-Hexanedioic Acid Diethyl Ester

37 g of 3-acetyl-4-oxo-pentanoic acid ethyl ester, synthesized accordingto the procedure given in Example 15, and 0.3 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene were mixed, and 30 g of ethylacrylate was added dropwise over 30 minutes. After stirring for 24hours, the base was neutralized by adding acetic acid. 80 ml of diethylether was added, and the mixture was extracted with 60 ml of an aqueoussodium carbonate solution and 150 ml of water. Fractional distillationof the water-free organic layer yielded 46.2 g of3,3-diacetyl-hexanedioic acid diethyl ester (boiling point: 150° C./0.03mbar; purity: >99%; colorless).

Content of the active structural element C₃O₂: 24%.

Example 10 3-Acetyl-3-(Ethoxycarbonyl)-Pentanedioic Acid 1,5-DimethylEster

86 g of potassium tert-butylate was dissolved in 150 ml of dimethylacetamide and 100 g of acetoacetic acid ethyl ester was added drop bydrop with stirring. Subsequently, 83 g of chloroacetic acid methyl esterwas added dropwise. When the exothermic reaction ended, 5 g of potassiumtert-butylate and 5 g of chloroacetic acid methyl ester were addedalternately until conversion was complete. The solid was filtered offand washed with ethyl acetate. Fractional distillation yielded 30 g of3-acetyl-3-(ethoxycarbonyl)-pentanedioic acid dimethyl ester (purity:91%; colorless)

Content of the active structural element C₃O₂: 25%.

Example 11 2-Acetyl-2-(Ethoxycarbonyl)-Hexanedioic Acid 1,6-DimethylEster

15 g of methyl acrylate was added dropwise to a mixture consisting of 30g of 2-acetyl-1,4-butyric acid dimethyl ester and 0.5 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene. The mixture was stirred at 75° C.for 4 hours. After cooling, it was neutralized with acetic acid, washedwith an aqueous potassium carbonate solution and was subsequently washedwith water, and distilled, and colorless2-acetyl-2-(ethoxycarbonyl)-hexanedioic acid dimethyl ester was obtainedat 95% purity.

Content of the active structural element C₃O₂: 25%

Example 12

4,4-Diacetyl Heptahedioic Acid 1,7-Diethyl Ester

20 ml of 2,4-pentandione, 40 ml of ethyl acrylate, and 1.5 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene were mixed, and stirred for 3 hoursat 80° C. in air. The crude product was distilled (boiling point: 155°C./10⁻² mbar). The distilled product was crystallized in rhombiccrystals having purity of 99.4% (gas chromatography). Melting point: 64°C. The product was colorless. Content of the active structural elementC₃O₂: 23%.

Example 13 4-Acetyl-4-(Methoxycarbonyl)-Heptanedioic Acid 1,7-DimethylEster

50.0 g of methyl acetoacetate and 100.0 g of methyl acrylate were mixed,and 0.6 g of tetramethyl guanidine and 0.05 g of 4-methoxy phenol wereadded. The mixture was stirred at 85° C. for 3 hours in air, and theexcess methyl acrylate was removed by distillation, leading to ayellowish liquid crude product with a purity of 91%. The finalfractional distillation of the crude product yielded the subjectcompound, which was colorless, having a boiling point: 145° C. (10⁻²mbar) and purity: GC>99%.

Content of the active structural element C₃O₂: 24%.

Example 14 4,4-Di-(1-Oxopropyl)-Heptanedioic Acid 1,7-Dimethyl Ester

40.0 g (0.465 mol) of methyl acrylate was added drop by drop to 21.9 g(0.171 mol) of 3,5-heptanedione and 0.2 g (1.3×10⁻³ mol) of DBU. Afteraddition of two thirds of the acrylate, temperature was raised to 40° C.Stirring was continued for three hours, then the mixtures was heated toreflux, and an additional 0.5 g (3.3×10⁻³ mol) of DBU was added.Refluxing was continued for 6 hours, excess acrylate was distilled off,and the product was isolated by fractional distillation. 22.8 g (0.08mol) of dimethyl 4,4-di-(1-oxopropyl)-heptanedioate was obtained(boiling temperature: 175° C. at 0.02 mbar; yield: 44%; colorless).

Content of the active structural element C₃O₂: 23%.

Example 15 4-(Methoxycarbonyl)-4-(1-Oxopropyl)-Heptanedioic Acid1,7-dimethyl ester

39.9 g (0.31 mol) of methyl 3-oxo-pentanoate and 1.9 g (0.012 mol) ofDBU were mixed at room temperature in a three necked round bottom flask,equipped with a dropping funnel and a reflux condenser. 66.4 g (0.77mol) of methyl acrylate was slowly added drop by drop. After theexothermal behavior has leveled off, the reaction mixture was stirred at60° C. for an additional two hours. Cyclohexane was added and themixture was washed with diluted hydrochloric acid and was subsequentlywashed with distilled water until the aqueous layer showed a neutralreaction. The organic layer was dried over sodium sulfate, the solventwas removed, and the addition product was isolated by fractionaldistillation in a vacuum. 21.4 g (0.20 mol) of4-(methoxycarbonyl)-4-(1-oxopropyl)-heptanedioic acid 1,7-dimethyl esterwas obtained (yield: 64%; boiling temperature: 130° C. at 0.02 mbar;colorless).

Content of the active structural element C₃O₂: 23%.

Example 16 4-(Ethoxycarbonyl)-4-(2-Methyl-1-Oxopropyl)-HeptanedioicAcid-1,7-Dimethyl Ester

12.0 g (0.08 mol) of ethyl 4-methyl-3-oxo-pentanoate and 0.5 g (0.003mol) of DBU were placed in a three necked round bottom flask,equipped-with dropping funnel and reflux condenser. At room temperature,16.0 g (0.18 mol) of methyl acrylate was slowly added drop by drop.After the exothermal behavior of the reaction leveled off, the reactionmixture was stirred at 60° C. for an additional two hours. The mixturewas poured into cyclohexane and was washed with diluted hydrochloricacid and was subsequently washed with distilled water until the aqueouslayer was neutral. The organic layer was dried over sodium sulfate, thesolvent was removed, and the addition product was isolated by fractionaldistillation in a vacuum. 15.0 g (0.045 mol) of4-(ethoxycarbonyl)-4-(2-methyl-1-oxopropyl)-heptanedioic acid1,7-dimethyl ester was obtained (yield: 56%; boiling point: 145° C. at0.02 mbar; colorless).

Content of the active structural element C₃O₂: 21%.

Example 17 4-(Ethoxycarbonyl)-4-(1-Oxobutyl)-Heptanedioic Acid1,7-Dimethyl Ester

41.2 g (0.26 mol) of ethyl 3-oxo-hexanoate and 1.9 g (0.012 mol) of DBUwere placed in a three necked round bottom flask, equipped with droppingfunnel and reflux condenser. At room temperature, 56.3 g (0.65 mol) ofmethyl acrylate was slowly added drop by drop. After the exothermalbehavior of the reaction leveled off, the reaction mixture was stirredat 60° C. for an additional two hours. The mixture was poured intocyclohexane and was washed with diluted hydrochloric acid and wassubsequently washed with distilled water until the aqueous layer showeda neutral reaction. The organic layer was dried with sodium sulfate, thesolvent was removed, and the residual addition product was isolated byfractional distillation in a vacuum. 50.0 g (0.15 mol) of4-(ethoxycarbonyl)-4-(1-oxobutyl)-heptanedioic acid 1,7-dimethyl esterwas obtained (yield: 58%; boiling point: 149° C. at 0.007 mbar;colorless).

Content of the active structural element C₃O₂: 21%.

Example 18

3,3-Diacetyl-1,5-Dicyanopentane

After addition of 0.25 g of KOH, dissolved in 2.5 ml of methanol, to15.0 g of 2,4-pentandione, 35.0 g of acrylonitrile was added dropwisewith the reaction temperature not exceeding 40° C. The product which wasprecipitated during the process was filtered off, washed with a smallamount of acetone, and dried. Melting point: 185-186° C. Purity >98%.The product was colorless.

Content of the active structural element C₃O₂: 33%.

Example 19 5,5-Diacetyl Nonane-2,8-Dione

A mixture of 15.0 g of 2-4-pentandione and 0.35 g of tetramethylguanidine was added to 40.0 g of 2-butanone drop by drop, with thereaction temperature not exceeding 40° C. Then, the excess of 2-butanonewas removed by distillation under reduced pressure (200 mbar). The finalproduct was obtained at 96% purity as a colorless product. Meltingpoint: 59° C. Content of the active structural element C₃O₂: 28%.

Example 20 4,4-Diacetyl-Heptanedioic Acid 1,7-Di-Tert-Butyl Ester

At room temperature, 282 g of tert-butyl acrylate was added dropwise toa mixture of 100 g of 2,4-pentandione and 3 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene and stirred for 5 hours. A smallportion of methanol was added to the mixture at 40° C. A crude productwas precipitated from the mixture at room temperature and wasrecrystallized from methanol to obtain 4,4-diacetyl-heptanedioic aciddi-tert-butyl ester as white crystals at a yield of 54% (purity: 100%;colorless).

Content of the active structural element C₃O₂: 20%.

Example 21 4,4-Diacetyl-1,7-Heptanedioic Acid

4,4-Diacetyl-heptanedioic acid di-tert-butyl ester was hydrolyzed at 95°C. over 5 hours using a mixture of tert-butanol and water as solvent and11 weight-% hydrochloric acid. The solvent was removed and the obtainedcrude product was recrystallized from a mixture of acetone and petroleumether (1:1) to yield 4,4-diacetyl-heptanedioic acid as white crystals ata yield of 69%. (melting point: 176° C.; purity 94%; colorless).

Content of the active structural element C₃O₂: 28%.

Example 22 3,3-Diacetyl-1,5-Bis(Methylsulfonyl)-Pentane

6 g of 2,4-pentandione and 3 drops of triethyl amine were mixed and 7 gof methyl vinyl sulfone was added dropwise at room temperature. Afterstirring at 60° C. for 7 hours, 5 drops of1,8-diazabicyclo-[5.4.0]-undec-7-ene were added and the mixture wasstirred at room temperature for 12 hours. The mixture was stirred with25 ml of ethanol and neutralized after a white solid was precipitated.The mixture was poured into 200 ml of water and ice, and was kept in therefrigerator overnight. The solvent was-filtered off, dried andrecrystallized from 500 ml of ethanol. 2.9 g of white, long needles ofthe subject compound was obtained (melting point: 162° C.; purity: >99%;colorless).

Content of the active structural element C₃O₂: 22%.

Example 23 4,4-Diacetyl-7-Oxo-Octanoic-Ethyl Ester

60 g of 2,4-pentandione and 0.1 g of triethyl amine were mixed, and 28 gof 2-butanone was added dropwise at room temperature. The mixture wasstirred for 42 hours and the raw product was distilled off.Re-distillation gave 31.4 g of 3-acetyl-2,6-heptandione.

10.2 g of 3-acetyl-2,6-heptandione and 5 drops of1,8-diazabicyclo-[5.4.0]-undec-7-ene were mixed, and 9 g of ethylacrylate was added dropwise over 15 minutes. After stirring for 16hours, the base was neutralized with acetic acid, 30 ml of diethyl etherwas added, and the solution was extracted with sodium carbonate solutionand water. Fractional distillation of the dry organic layer yielded 9.3g of 4,4-diacetyl-7-oxo-octanoic-ethyl ester (boiling point: 136°C./0.02 mbar; purity: 81%; colorless).

Content of the active structural element C₃O₂: 26%.

Example 24 4,4-Diacetyl-5-(Ethoxycarbonyl)-Heptanedioic Acid DiethylEster

a) To a mixture of 70 g of 2,4-pentandione and 1.72 g of trioctylphosphine, 45 g of ethyl acrylate was added dropwise over 40 minutes,keeping the temperature at 0-5° C. by cooling. After stirring for 65hours, 2 ml of acetic acid and 150 ml of diethyl ether were added, andthe solution was extracted with an aqueous sodium carbonate solution andwater. The organic layer was dried, and 4-acetyl-5-oxohexanoic acidethyl ester was isolated by fractional distillation.

b) 25.7 g of 4-acetyl-5-oxohexanoic acid ethyl ester and 0.3 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene were mixed, and 35 g of fumaricacid diethyl ester was added at room temperature over 40 minutes. Afterstirring for 24 hours, the amount of1,8-diazabicyclo-[5.4.0]-undec-7-ene was doubled and stirring continueduntil conversion was complete. 0.5 g of acetic acid and 50 ml of diethylether were added, and the solution was extracted with an aqueouspotassium carbonate solution and water. Fractional distillation of thedry organic layer yielded 25.6 g of4,4-diacetyl-5-(ethoxycarbonyl)-heptanedioic acid diethyl ester (boilingpoint: 170° C./0.002 mbar; purity: 93%; colorless). Content of theactive structural element C₃O₂: 18%.

Example 25 4-Acetyl-4-(Methoxycarbonyl)-Octanedioic Acid 1,8-DimethylEster

0.3 g of sodium was dissolved in 160 g of methyl acetoacetate, and 86 gof methyl acrylate was added drop by drop at a temperature below 30° C.The reaction was continued for one hour, and subsequently the pH wasadjusted to 7. The salt was filtered off and the raw product purified bydistillation to yield 2-acetyl pentanoic 5-ethyl-1-methyl ester.

12.5 g of 1,8-diazabicyclo-[5.4.0]-undec-7-ene and 2.3 sodium weredissolved in 50 g of 2-acetyl pentanoic 5-ethyl-1-methyl ester, and 48 gof bromobutyric acid ethyl ester was added drop by drop. When thetemperature decreased, an additional 2 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene was added. After almost all eductwas consumed, the salt was filtered off and4-acetyl-4-(methoxycarbonyl)-octanedioic acid dimethyl ester wasisolated by fractional distillation to yield 44 g of colorless product(purity: 94%).

Content of the active structural element C₃O₂: 21%.

Example 26 4-Acetyl-4-(Tert-Butoxycarbonyl)-Heptanedioic Acid1,7-Dimethyl Ester

0.5 g of 1,8-diazabicyclo-[5.4.0]-undec-7-ene and 40 g of tert-butylacetoacetate were stirred at room temperature. 60 g of methyl acrylatewas dropped in. The exothermic reaction started immediately. Thetemperature of the mixture was allowed to reach 80° C. The mixture wasstirred at 80° C. for an additional two hours. The basic catalyst wasremoved by washing with diluted hydrochloric acid and the organic layerwas fractionated in a vacuum. The pure colorless4-acetyl-4-(tert-butoxycarbonyl)-heptanedioic acid 1,7-dimethyl esterboils at 149° C./0.025 mbar (yield: 56 g).

Content of the active structural element C₃O₂: 21%.

Example 27 1,1,1-Triacetylethane

3-methylpentanedione-2,4 was prepared from acetylacetone and methyliodide in the presence of potassium carbonate (Organic Syntheses, Coll.Vol. V, 785).

57 g of 3-methylpentanedione-2,4 was treated with-12 g of sodiumhydride. During this process, the temperature was maintained at 30-40°C. Then, 200 ml of diethyl ether was added, and 39.25 g of acetylchloride was dropped in. The mixture was stirred for 3 hours in boilingether and was washed with potassium hydroxide. Diethyl ether wasdistilled off in a vacuum. The residual slightly yellowish liquid wasthe crude triacetyl ethane having a purity of above 90%.

Content of the active structural element C₃O₂: 44%.

Example 28 4,4-Diacetyl-5-Oxohexanoic Acid Methyl Ester

4-acetyl-5-oxohexanoic acid methyl ester was prepared through theMichael addition of methyl acrylate to acetyl acetone in the presence ofmetallic sodium. The crude product was purified by vacuum distillationand received in a purity of approximately 99%.

92.5 g of 4-acetyl-5-oxohexanoic acid methyl ester was reacted with 11.5g of metallic sodium in 200 ml of diethyl ether. After the dissolving ofsodium was finished, 39.25 g of acetyl chloride was dropped in, and theresulting boiling mixture was stirred for 6 hours. Then, the reactionmixture was filtered, washed with aqueous potassium hydroxide and water,following by evaporation of solvent. The final vacuum distillationyielded the subject compound as a yellowish liquid having a purity ofabove 90%.

Content of the active structural element C₃O₂: 30%.

Example 293-{4-Acetyl-4-[2-(Ethoxycarbonyl)Ethyl]-5-Oxohexanoyloxy}-2,2-DimethylpropylEthyl 4,4-Diacetylheptane-1,7-Dioate

5.0 g of 4-acetyl-5-oxohexanoic acid ethyl ester and five drops1,8-diazabicyclo-[5.4.0]-undec-7-ene were mixed and 2.6 g of neopentylglycol diacrylate was added dropwise. The mixture was stirred for threehours to yield a highly viscous colorless oil. Gel permeationchromatography showed a main peak at 690 g/mol, nuclear magneticresonance spectra and infrared spectrum are according to the expectedstructure.

Content of the active structural element C₃O₂: 22%.

Example 302,2-Bis({4-Acetyl-4-[2-(Ethoxycarbonyl)Ethyl]-5-Oxohexanoyloxy}Methyl)ButylEthyl 4,4-Diacetylheptane-1,7-Dioate

5.0 g of 4-acetyl-5-oxo-hexanoic acid ethyl ester and five drops1,8-diazabicyclo-[5.4.0]-undec-7-ene were mixed, and 2.4 g oftrimethylolpropane triacrylate was added dropwise. The mixture wasstirred for three hours to yield a highly viscous colorless oil. Gelpermeation chromatography showed a main peak at 958 g/mol, and nuclearmagnetic resonance spectra and infrared spectrum were according to theexpected structure.

Content of the active structural element C₃O₂: 23%.

Example 31 Dimethyl4-Acetyl-4-[(3-{2,2-Bis(2-(Methoxycarbonyl)Ethyl]-3-Oxobutanoyloxy}-2,2-Dimethylpropyl)Oxycarbonyl)Heptane-1,7-Dioate

Transesterification of neopentylglycol with ethyl acetoacetate yieldedneopentylglycol diacetoacetate. The crude product was isolated through ashort-path distillation (110° C. at 0.001 mbar) to yield the pure (>98%)neopentylglycol diacetoacetate as a colorless liquid.

40 g of this diacetoacetate and 0.4 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene were stirred at room temperature,and 100 g of methyl acrylate was added drop by drop. After the firstexothermic reaction finished, the mixture was stirred for 3 hours at 80°C. Then, the excess of methyl acrylate was distilled off in a vacuum.The subject compound remained as a slightly yellowish viscous liquid.Yield was 88 g. Nuclear magnetic resonance spectra and infrared spectrumconfirmed the expected structure.

Content of the active structural element C₃O₂: 22%.

Example 32 Photoinitiator Based on Pentaerythritol Tetraacetoacetate andEthyl Acrylate

100 g of ethyl acrylate and 2 g of 10% methanolic KOH were added to 50 gof a tetra acetoacetate, synthesized by transesterification ofpentaerythritol with ethyl acetoacetate. The mixture was stirred for 3hours at 80° C. Subsequently the basic catalyst was neutralized withacetic acid. The resulting crude reaction product was a highly viscous,yellowish oil. Molecular weight Mw=860 (GPC)

Content of the active structural element C₃O₂: 21%.

Example 333-{(4S)-4-(Ethoxycarbonyl)-4-[2-(Ethoxycarbonyl)Ethyl]-5-Oxohexanoyloxy}-2,2-DimethylpropylEthyl (4S)-4-Acetyl-4-(Ethoxycarbonyl)Heptane-1,7-Dioate (PhotoinitiatorBased on NPGDA and Acetyl Diethylglutarate)

46 g of acetylglutaric acid diethyl ester and 0.5 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene were stirred at room temperature,and 21.2 g of neopentylglycol diacrylate was added drop by drop. Afterthe first exothermic reaction finished, the mixture was stirred for 3hours at 80° C. The subject compound remained as a slightly yellowishviscous liquid. Yield was 66.5 g. Nuclear magnetic resonance spectra andinfrared spectrum confirmed the expected structure.

Content of the active structural element C₃O₂: 20%.

Example 342,2-Bis({4-(Methoxycarbonyl)-4-[(Methoxycarbonyl)Methyl]-5-Oxohexanoyloxy}Methyl)ButylMethyl 3-Acetyl-3-(Methoxycarbonyl)Hexane-1,6-Dioate (PhotoinitiatorBased on TMPTA and Acetyl Dimethylsuccinate)

56.4 g of acetylsuccinic acid dimethyl ester and 0.5 g of1,8-diazabicyclo-[5.4.0]-undec-7-ene were stirred at room temperature,and 30 g of trimethylolpropane triacrylate was added drop by drop. Afterthe first exothermic reaction finished, the mixture was stirred for 3hours at 80° C. The subject compound remained as a slightly yellowishviscous liquid. Yield was 86 g. Nuclear magnetic resonance spectra andinfrared spectrum confirmed the expected structure.

Content of the active structural element C₃O₂: 24%.

Comparative Example 1

0.10 mol of 2,4-pentandione, 0.195 mol of tripropylenglycol diacrylate,and 0.45 g of tetramethylguanidine were mixed and stirred under spargingwith air. After the reaction had started, the temperature was allowed toreach 90° C. Then the mixture was cooled to 80° C. and stirred at thistemperature for one hour. After cooling, the product had a viscosity of12000 mPas at 25° C. and a molecular weight of Mw=2000.

Content of the active structural element C₃O₂: 9.86%.

Comparative Example 2

50.0 g of trimethylolpropane triacrylate, 50 g of tripropylene glycoldiacrylate, and 15.0 g of ethyl acetoacetate were mixed, and this washeated to 50° C. before 1.5 g of 1,8-diazabicyclo-[5.4.0]-undec-7-ene(DBU) was added. The mixture was sparged with air. After the exothermicreaction started, the temperature was allowed to rise until 110° C.Then, the mixture was cooled to 80° C. and stirred for 1 hour at 80° C.After cooling, the resulting product had a viscosity of 18000 mPas at25° C. and a molecular weight of Mw=6000.

Content of the active structural element C₃O₂: 6.73%.

(Properties of Cured Coatings)

The following table shows properties of various cured coatings ofphotocurable compositions which contain photinitiators from theabove-mentioned examples.

Fist of all, photocurable compositions were prepared by mixing thecomposition in the table, then coated on aluminum sheets as thin filmsand cured by UV irradiation.

The cured coatings were tested with respect to their pencil hardness andtheir solvent resistance towards ethyl methyl ketone. Table:Photoinitiator concentration exposure solvent pencil System from example(weight %) test substance energy¹ resistance² hardness³ 1 12 3UV-overprint 0.6 J/cm² >75 H-2H varnish⁴ 2 12 7 UV-overprint 0.6J/cm² >75 2H-3H varnish⁴ 3 13 8 UV-overprint 0.6 J/cm² ˜30 HB varnish⁴ 412 5 epoxy acrylate⁵ 0.6 J/cm² >75 3H 5 12 5 polyester acrylate⁶ 0.6J/cm² >75 H 6 13 10 polyester acrylate⁶ 0.6 J/cm² >75 H  7⁸ 18 3 epoxyacrylate⁷ 0.1 J/cm² >75 4H 8 19 5 Acrylate mixture⁹ 0.5 J/cm² >100 2H¹Quantity of light for crosslinking produced by a F 300H-lamp (SumUV-A-B-C), measured with a radiometer from EIT.²Solvent resistance of the cured film, tested by repeatedly rubbing thecured surface with a cotton sheet soaked in ethyl methyl ketone (MEK).The number of recurrences, the so called double-rubs, performed withoutvisible damage on the film was counted³Hardness of pencil which caused visual damage on the cured film⁴UV-overprint varnish, consisting of 40% tripropylene glycol diacrylate,30% (trimethylolpropane) triacrylate and 30% bisphenol A diglycidyletherdiacrylate.⁵Epoxy acrylate Ebecryl 120 from UCB.⁶Polyester acrylate Ebecryl 835 from UCB.⁷Epoxy acrylate, obtained by reacting Epiclon 1050 from DIC with acrylicacid.⁸Curing was done at 110° C., as the curable mixture is solid at 25° C.⁹Acrylate mixture comprising 30% by weight of Dipropyleneglycoldiacrylate (DPGDA), 45% by weight of an acrylate compound obtained byreacting Epiclon 1050 from DIC with acrylic acid, and 25% by weight ofTrimethylolpropane triacrylate (TMPTA).

The photoactivity of all prepared photoinitiators was tested.

For UV-curing tests, a mixture consisting of 30 weight-% tripropyleneglycol diacrylate (TPGDA), 25 weight-% trimethylolpropane triacrylate(TMPTA) and 45 weight-% Ebecryl 150 (UCB) was used. A solution of 5weight-% of the tested photoinitiator in the UV-curable mixture wasprepared and coated on an aluminum sheet as a film of 50 μm thickness.The sample was irradiated with a Fusion F 300 using the H-bulb (300W/inch). The radiation doses were 0.087 J/cm² for UV-A, 0.058 J/cm² forUV-B and 0.035 J/cm² for UV-C, which gives 180 mJ/cm² in sum. Thebelt-speed was adjusted to 16 m/min and 3 passes were done.

All tested photoinitiators of the invention are photoactive and initiatea polymerization under irradiation, indicated by the formation ofsolvent-resistant films. The solvent resistance of the cured film wastested by rubbing the film with a cotton sheet soaked with 2-butanone(methyl ethyl ketone; MEK) and counting the double rubs needed to causevisible defects in the film. The results are summarized in the followingtable: Photoinitiator Solvent resistance of the according to cured film(MEK double example No. rubs)  1 >100  2 >100  3 >100  4 ˜12  5 >100  6˜13  7 ˜32  8 ˜28  9 >100 10 >100 11 >100 14 ˜40 15 ˜42 16 ˜52 17 ˜20 19^(a)) >100 20 >100  21^(b)) >100  22^(c)) >80 23 >100 24 >100 25 ˜4026 ˜60 27 >100 28 ˜14 29 >100 30 >100 31 ˜60 32 ˜70 33 <80 34 <100^(a))a test mixture consisting of 29% dipropylene glycol diacrylate(DPGDA), 42% Ebecryl 150 and 24% TMPTA was used^(b))a solution of 4 weight % of the photoinitiator in a mixture of 20%deionized water and 76% Photomer 3165 (Cognis) was tested^(c))10 weight % of dimethyl sulfoxide were added to the test mixture inorder to dissolve the photoinitiator

As a reference, a film of the same thickness was coated on the samesheet consisting of the UV-curable mixture, however, without aphotoinitiator of the present invention. This film showed no curing andwas easily removed by whipping with a dry cotton sheet.

Also, the influence of the molecular weight of the photoinitiators ontheir photoactivity was investigated.

-   -   Substrate: Aluminum    -   Film Thickness: 50 μm (wet)    -   ¹Irradiance: 0.5 J/ cm²    -   Bulb: Fusion F 300H bulb    -   Test-mixture: Standard UV over-print varnish:        -   Dipropyleneglycol diacrylate (DPGDA) 30%        -   Acrylated polyester Ebecryl 150 45%        -   Trimethylolpropane triacrylate (TMPTA) 25%

Procedure: The photoinitiators were dissolved in the test mixture. Thetest mixture was applied on an aluminum substrate at a film thickness of50 μm (wet) and cured under UV-light with a Fusion F 300 H bulb. Theapplied irradiance was 0.5 J/cm². Then, the coatings were assessed byappearance, solvent resistance and hardness. ²PI- ³Coating Surface⁴Solvent ⁵Pencil Molecular Entry Type % PI viscosity appearanceresistance hardness weight 1 — — 200 mPas wet 0 — 2 A 5 200 mPasdry >100 2H 240 3 B 5 200 mPas dry >100 2H 300 4 C 5 260 mPas wet ˜5 <6B1800 5 C 13.7 290 mPas wet-tacky ˜25 HB 1800 6 C 24.2 340 mPastacky >100 H 1800 7 C 32.4 540 mPas dry >100 H-2H 1800¹Radiant energy of the UV-bulb (total UVA-C) at the surface of thecoating measured with the radiometer UVICURE from EIT company.²PI type:A = 5,5-diacetylnonane-2,8-dione, (Example 19 of this invention)B = diethyl-4,4-diacetylheptanedioate, (Example 12 of this invention)C = photoactive resin prepared according to U.S. Pat. No. 5945487,column 9, line 45.³Coating viscosity, measured with an ICI cone and plate viscosimeter ata shear rate of 5000 D⁻¹⁴Solvent resistance of the hardened film, tested by repeated rubbing ofthe film surface with a woodpulp cloth impregnated with methyl ethylketone (MEK). The number of rubbings that still did not produce anyvisible damage to the coating was measured.

(properties comparison with conventional phoinitiators) 2-hydroxy-2-methylpropio- Bisacylphenyl Photoinitiator Example 19 phenonephosphineoxide Color Colorless slightly slightly yellow yellow Molarextinction 122 ml/g · cm 822 ml/g · cm 18200 ml/g · cm coefficients at300 nm in methanol

Due to the low molar extinction coefficient, photoinitiators of thepresent invention are particularly suitable for curing of thick coatingslayers, which was demonstrated by the following experiment:

A container, having dimensions of 1 cm×1 cm×1 cm, was filled with a testmixture, containing 30% of trimethylolpropane triacrylate, 30% ofbisphenol-A-diglycidylether diacrylate, 35% of dipropylene glycoldiacrylate and 5% of 5,5-diacetylnonane-2,8-dione (a photoinitiatoraccording to Example 19 of the present invention). Then, the containerwas irradiated from above with a Fusion F300 H bulb (Irradiance >0.25J/cm²). After the curing process, the content of the container, whichcontains a cured thick layer on top and uncured liquid material beneath,was removed, and the thickness of the cured top layer was measured by amicrometer screw. Thickness of the cured layer: 800 μm.

INDUSTRIAL APPLICABILITY

The photoinitiator according to this invention is usable for curing ofradical curable monomers, oligomers, or polymers.

The photocurable composition of the invention may be used as coatings,printing inks and molded articles. In particularly, the photocurablecomposition is usable as a coating composition for thick layers ofmultifunctional acrylic ester groups containing mixtures. That is, thephotocurable composition of the invention is characterized in that thecomposition exhibits excellent photosensitivity even when the coatedlayer has a thickness of up to 1000 μm.

As coatings, the composition can be applied to suitable substrates suchas, for example, paper, polyethylene, polypropylene, polyester,polyvinylidene chloride, aluminum, steel or wood and be cured byUV-irradiation in the presence of air or a cover gas.

Among these applications, of particular importance is a coating fordurable wood, can coating, or printing ink.

According to this invention, a photoinitiator can be provided, whichexhibits excellent photosensitivity, and is usable in thick layer UVcurable coatings.

1: A photoinitiator consisting essentially of a compound having amolecular weight of 1000 or less, and having a chemical structurerepresented by formula (1),

wherein R₃ and R₄ independently denote an alkyl group having a carbonnumber of 1 to 8, and R₁ and R₂ independently denote 1) an electronattracting group, 2) an alkyl group having a carbon number of 1 to 8, or3) an alkyl group having a carbon number of 1 to 8, which has anelectron attracting group at the β, γ, or δ position with respect toboth of the carbonyl groups, wherein the alkyl group 2) is methyl orethyl group when each of the two substituents is the alkyl group 2), andweight percentage of a chemical structure element represented by thefollowing formula (2),

which is expressed in formula (1), based on the total molecular weightof the compound, is within the range of 17% to 54% by mass. 2: Aphotoinitiator consisting essentially of a compound having a molecularweight of 1000 or less, and having a chemical structure represented bythe following formula (3),

wherein R₃ denotes an alkyl group having a carbon number of 1 to 8, R₅denotes a mono-, di-, tri-, tetra- or pentavalent aliphatic hydrocarbongroup, or an alkyleneoxy group containing aliphatic hydrocarbon group, nis a natural number of 1 to 5, and R₁ and R₂ independently denote 1) anelectron attracting group, 2) an alkyl group having a carbon number of 1to 8, or 3) an alkyl group having a carbon number of 1 to 8, which hasan electron attracting group at the β, γ, or δ position with respect toboth of the carbonyl groups, wherein the alkyl group 2) is methyl orethyl group when each of the two substituents is the alkyl group 2), andweight percentage of a chemical structure element represented by thefollowing formula (2),

which is expressed in formula (3), based on the total molecular weightof the compound, is within the range of 17% to 47% by mass. 3: Aphotoinitiator according to claim 1, wherein the R₁ and R₂ areidentical. 4: A photoinitiator according to claim 1, wherein thecompound has at least one chemical structure element represented by thefollowing formula (5).

5: A photoinitiator according to claim 2, wherein the compound has atleast one chemical structure element represented by the followingformula (6).

6: A novel compound having a chemical structure represented by thefollowing formula (7),

wherein R₆ denotes an alkyl group having a carbon number of 1 to 8, aC₁₋₄ alkyl carbonyl group, a cyano group, a C₁₋₄ alkyl carbonyl methylgroup, a C₁₋₄ alkyl carbonyl ethyl group, a C₁₋₄ alkoxy carbonyl methylgroup, a C₁₋₄ alkoxy carbonyl ethyl group, and an alkyl group having acarbon number of 1 to 8 which is substituted by carboxyl group or cyanogroup, R₇, R₈, R₉, and R₁₀ independently denote a hydrogen atom, or amethyl group, and at least one of R₉ and R₁₀ is a hydrogen atom, R₁₁denotes a di-, tri- or tetra-valent aliphatic hydrocarbon group having acarbon number of 2 to 12, R₁₂ denotes a methyl group, or an alkoxy grouphaving a carbon number of 1 to 18, n is a natural number of 2 to 4, andm is an integer of 0 to
 15. 7: A photocurable composition comprising,(i) a photoinitiator according to the claim 1, and (ii) a radicalcurable ethylenic unsaturated compound. 8: A photoinitiator according toclaim 2, wherein the R₁ and R₂ are identical. 9: A photocurablecomposition comprising, (i) a photoinitiator according to the claim 2,and (ii) a radical curable ethylenic unsaturated compound. 10: Aphotocurable composition comprising, (i) a photoinitiator according tothe claim 3, and (ii) a radical curable ethylenic unsaturated compound.11: A photocurable composition comprising, (i) a photoinitiatoraccording to the claim 4, and (ii) a radical curable ethylenicunsaturated compound. 12: A photocurable composition comprising, (i) aphotoinitiator according to the claim 5, and (ii) a radical curableethylenic unsaturated compound. 13: A photocurable compositioncomprising, (i) a photoinitiator according to the claim 6, and (ii) aradical curable ethylenic unsaturated compound. 14: A photocurablecomposition comprising, (i) a photoinitiator according to the claim 8,and (ii) a radical curable ethylenic unsaturated compound.